1. Field of the Invention
The present invention relates to solid-state imaging apparatus.
2. Description of the Related Art
As MOS-type solid-state imaging apparatus, a configuration having pixels arranged in a two-dimensional array, each column of which is provided with a signal holding capacitor and switch unit of the signal holding capacitor, is disclosed (Japanese Patent Application Laid-Open No. 2001-230974). Also, a configuration having an operational amplifier, a signal holding capacitor, and switch unit of the signal holding capacitor provided for each column as a unit of restraining amplification of a random noise by amplifying a signal in order to improve the signal-to-noise ratio of the solid-state imaging apparatus is disclosed (Japanese Patent Application Laid-Open No. 2008-278460). Further, Japanese Patent Application Laid-Open No. 2008-263298 discloses the use of a CMOS switch as the switch of signal holding capacitors. By using a CMOS switch as the switch of the signal holding capacitors, the configuration can load a higher voltage to the signal holding capacitors than the configuration using only the NMOS transistor as the switch does, thereby can increase the dynamic range in the signal holding capacitors.
The inventors found an issue that when an intensive spotlight is incident on a pixel area in the configuration, which uses CMOS switches as the switches of the signal holding capacitors, a white or black stripe results on either side of the spot. It is found that this problem is caused by the fact that not all the NMOS transistors and the PMOS transistors, which compose the CMOS switches in the whole area of the imaging plane, transit from the conducting state to the non-conducting state at the same timing.
It is generally known that a change in the electric potential of the gate during the turning on/off of the NMOS transistors and the PMOS transistors leads electric potential fluctuation at the drain side via the MOS transistor parasitic. If the NMOS transistor and the PMOS transistor are turned off almost at the same time, the electric potential fluctuation is canceled in the CMOS switch. If one CMOS switch is turned off earlier than the other CMOS switch, however, the signal electric potential loaded in the drain or source of the transistor fluctuates when the later CMOS switch is turned off. If this fluctuation equally occurs in the whole imaging area, neither a white stripe nor a black stripe occurs. It is found that if the NMOS transistors and the PMOS transistors are turned off almost at the same time in one area but not turned off at the same timing in the other area in the entire imaging area, the electric potential of the loaded signal differs between the two areas, which causes such a phenomenon as a white stripe and a black stripe.
When many of the pixels output signals which are biased to specific electric potential like an intensive spotlight, either the NMOS transistors or the PMOS transistors are turned on. Since the MOS transistor has the bigger gate parasitic in the off state than in the on state, there will be a significant difference in the parasitic between the control line which has many on-state MOS transistors connected thereto and the control line which has many off-state MOS transistors connected thereto. That causes a delay in pulses transmitting through the control lines, thereby causes a difference in the on/off timing between the NMOS transistors and the PMOS transistors. In that manner, an intensive spotlight causes a white stripe and a black stripe in an image.